Aesthetics: LED bar graph in Aluminium panel

[rs20]

Suppose I am getting an aluminium panel laser-cut and anodized to serve as the front panel on my audio-themed widget. I'd like a audio-level meter, based on the classic LED bar graph:



However, every LED bar graph that I can find has a reflective, white surface on each LED as shown in the image above. Now IIUC the typical intention is to put a dark window or film over the entire front panel (typically printed with dB figures etc etc) which darkens everything down and then the super-bright LEDs shine through that darkening and it all ends up looking sweet and awesome. However, I don't need printed numbers, and would prefer to skip this whole printing/film application process entirely. Are "pre-darkened" bar graph modules available? What keyword am I after?

I've also considered getting individual holes cut for separate rectangular through-hole LEDs, but this feels like a very fiddly and fragile approach.

So, I'm kind of failing to find something that's easy and elegant-looking. Any suggestions would be most gratefully accepted.

[Tomorokoshi]

Digi-Key seems to use the term "tinted" to describe something like that:

https://www.digikey.com/products/en/optoelectronics/leds-circuit-board-indicators-arrays-light-bars-bar-graphs/106?k=tinted&k=&pkeyword=tinted&pv207=663&pv207=664&pv207=666&pv207=528&FV=ffe0006a%2C1f140000&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Unfortunately most of the images are renderings, not photographs, and the datasheets don't really seem to specify anything.

[james_s]

You could put a sheet of thin tinted plexi behind the aluminum panel, that stuff is not hard to get and would probably look ok.

[sokoloff]

I use automotive cling window tint to knock down the intensity of LEDs on AV equipment. For your application, it should work well. Remember, that the ambient light has to pass through the tint twice to reflect off the LED substrate but the desired LED illumination only needs to pass through once. That means, start with a light (higher transmission rating) tint. I mostly use 20% and never use 5% (after testing it once). They're cheap and each roll is pretty much a multiple lifetime supply.

Gila Cling Tint (35% transmission), 20% transmission, or 5% transmission.

[sokoloff]

I didn't have the same part you're using handy, but I did have an LED matrix handy.

Here's a pic of the matrix with a 20% triangle and a 5% triangle of the Gila film over it. It's just laying on it for the picture, but you could get a smooth application easily enough.

[mariush]

There are some films which work sort of like the zebra strips on lcds, only allowing light vertically or something like that.

Here's an example , jump to around 40:20 :



So I suppose you could have some transparent sheet printed with something (for example to simulate a dot matrix or something like that) and put that over the led bar segments, and then over the film you could put a sheet of this material which would make everything that's not light basically the same color.

                                 

[QuantumLogic]

Like sokoloff, I used tinted vinyl for the LED displays on my homemade portable power supply project.  Not sure the tint percentage since I got it from eBay but 15 to 20% could be right.

[Buriedcode]

Whilst LED displays often use tinted plastic to increase contrast, the best (and most common) used for car dashboards is a circular polariser - that strongly attenuates lights that has passed through it twice, like reflections.  The effect is, light being emitted is subject to 50% attenuation, as with any polariser, but light entering the filter, reflecting off the diffuse surface of the segments, then coming back out of the filter, is attenuated.

The reason the segments appear reflective is because they use diffuse plastic, along with the white housing to form a light box, meaning a point-source (like an LED die) can provide even illumination over the entire segment.  So I very much doubt you will find 'dark' ones. There is no way around this, which is why tinted plastic (or the more expensive circular polariser) options are so common where VFD's aren't appropriate, and things have to be readable in fairly bright conditions.

I suspect the film in 'big clive's video is what I'm on about.  Great stuff!

[radar_macgyver]

Check out Avago/Broadcom Application Note 1015 for contrast enhancement techniques for LED displays.